Pileus clouds
What is Pileus clouds?
Pileus clouds (6000-9000m, High clouds) are
smooth formation found at the top of cumulus congestus or cumulonimbus clouds.
How to form?
A pileus cloud is formed by strong updrafts associated with a growing cumuliform cloud. These updrafts, which reach speeds of 20 to 30 mph (32 to 48 kph), force a parcel of air sharply upward. The air parcel travels along the side of the cumuliform cloud and over the top. It settles above the cloud, where the moisture within the air condenses into a flat, elongated cloud. If the cumuliform cloud continues to grow taller, it will touch the pileus cloud, making it appear that the cumuliform cloud is wearing a pileus cap.